Protein electrophoresis and immunofixation electrophoresis are key techniques to identifiy protein abnormalities and to detect abnormal immunoglobulins (paraproteins) in body fluids. Paraproteins are the products of clonal or oligoclonal proliferation of plasma cells and, as such, may represent full immunoglobulins, free heavy chains, and/or free light chains of immunoglobulins. Correct identification of paraproteins can be hampered, however, by the occurrence of pseudoparaproteins. Pseudoparaproteins are normally occurring proteins that mimic monoclonal-proteins in protein electrophoretic patterns. Over the past year, we have observed new cases of urine pseudoparaproteins that had not been described in the existing literature. Using a combination of various analytical techniques (e.g., electrophoresis in agarose and polyacrylamide gel, immunoelectrophoresis, and mass spectrometry), we identified additional cases of previously unknown pseudoparaproteins. In a collaborative study, we continue to assess the performance of protein electrophoresis and immunofixation electrophoresis as predictors for high-risk phenotype in familial Waldenstrom macroglobulinemia.